diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index afa8c67f..209ee3f4 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -107,6 +107,7 @@
   "queens.ml": 2,
   "quicksort.ml": 44,
   "roman.ml": 44,
+  "reverse_int.ml": 54329,
   "rpn.ml": 9,
   "run_decode.ml": 21,
   "run_length.ml": 11,
diff --git a/lib/ocaml/baseline/reverse_int.ml b/lib/ocaml/baseline/reverse_int.ml
new file mode 100644
index 00000000..7dc1bc97
--- /dev/null
+++ b/lib/ocaml/baseline/reverse_int.ml
@@ -0,0 +1,12 @@
+let reverse_int n =
+  let m = ref n in
+  let r = ref 0 in
+  while !m > 0 do
+    r := !r * 10 + !m mod 10;
+    m := !m / 10
+  done;
+  !r
+
+;;
+
+reverse_int 12345 + reverse_int 100 + reverse_int 7
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index 13ad9d44..993a5dab 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,11 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-10 Phase 5.1 — reverse_int.ml baseline (digit-reverse,
+  reverse(12345) + reverse(100) + reverse(7) = 54321 + 1 + 7 =
+  54329). Walks digits via mod 10 / div 10, accumulating the
+  reversed value. Trailing zeros collapse (reverse 100 = 1).
+  132 baseline programs total.
 - 2026-05-10 Phase 5.1 — bowling.ml baseline (10-pin bowling score
   for canonical "167" PBA-style game). Walks pin-knockdown list
   applying strike/spare bonuses through a 10-frame counter. Strike